The dial number (DN) set and enterprise are important properties of user IDs, trunks, call prefixes, and routes. User IDs manage user information. Trunks, call prefixes, and routes ensure that calls are connected and released properly.
Figure 1 Intra-office call
Intra-office call: Generally, a device is considered to be an exchange office. If both parties of a call are in the same exchange office, the call is an intra-office call.
Outgoing call: Voice signals are transmitted over the trunk between two exchange offices.